i don't think that reaching a 100% fluent level in another language is possible with just interacting with the same people as different people might have a slight difference way of speaking.
each place has their own unique twist in the way a language is structured and also slight different pronunciations.
traveling is the only way to 100% solve it, but if that's not possible interacting with media (like youtube videos, books, etc) in said language might help with less cost.
Even more so if those are related to things they like as it gives them a bigger incentive to want to understand them